The WO3 thin-film NOx sensor which is of practical use and includes the heater and the temperature sensor was fabricated. The WO3 thin films as a gas-sensing layer was deposited at ambient temperature in a high-vacuum resistance heated evaporator. The highest sensitivity of the WO3 thin-film sensor to NOx was obtained under the condition of the annealing temperature of 50$0^{circ}C$ and the operating temperature of 30$0^{circ}C$. The gas sensing characteristics of this sensor was excellent, i.e. high sensitivity (Rgas/Rair in 3 ppm NO2=53) and fast response time (4 seconds).